In the field of coating compositions, efforts have been made and are presently being made to increase the flexibility and hardness of cured coatings and finishes in order to make them more suitable for such uses as automotive finishes, appliance finishes, business machine finishes, house siding, general metal finishing and the like. The inclusion of epsilon caprolactone into coating compositions is known to increase the flexibility of the coating films. See, for example, U.S. Pat. No. Re. 30,234 in which epsilon caprolactone is reacted with a copolymer, e.g., styrene and 2-hydroxyethyl acrylate, and thereafter with a crosslinking agent, e.g., melamine formaldehyde, to give a crosslinked modified copolymer having desirable flexibility, hardness and chemical durability. The polymeric compositions of the present invention utilize novel compositions containing a reactive monomer derived from the reaction product of a hydroxyalkyl acrylate or methacrylate and a lactone, e.g., epsilon caprolactone, which can polymerize with other ethylenically unsaturated monomers and thereafter can be crosslinked to give polymeric coating compositions having a highly desirable combination of flexibility and hardness in addition to excellent adhesiveness, hydrolytic stability, chemical compatibility and solvent resistance. The novel compositions containing a reactive monomer derived from the reaction product of a hydroxyalkyl acrylate or methacrylate and a lactone, e.g., epsilon caprolactone, are described more fully in U.S. Patent Application Ser. No. 438,496, filed on Nov. 2, 1982, now abandoned, and in copending U.S. Patent Application Ser. No. 565,530, filed Dec. 29, 1983.
U.S. Pat. No. 3,655,631 describes, as in Example 1 thereof, the polymerization of epsilon-caprolactone with hydroxyethyl acrylate as initiator in the presence of 0.1% by weight of p-toluene sulphonic acid as catalyst at a temperature of 45.degree. C. for a time of 4 hours. The catalyst is described as an organic acid catalyst selected from the group consisting of halogen substituted aliphatic carboxylic acids other than trichloroacetic acid, alkane sulphonic acids, benzene sulphonic acid and lower alkyl substituted benzene sulphonic acids. The product is described in said Example I as a solid unsaturated polyester having a molecular weight of about 960. Example 8 of said patent describes the polymerization of hydroxyethyl methacrylate and epsilon-caprolactone using 0.1% by weight of p-toluene sulphonic acid catalyst. The polyester product is described as having a molecular weight of 437 and being a viscous liquid. The polyesters produced in said patent have residual acid catalyst present in relatively large amounts (i.e., about 1000 parts per million). In Examples 1 and 8 the described polymerization is stated to be complete. The epsilon caprolactone.hydroxyethyl acrylate product of Example 1 was further copolymerized with styrene (Examples 2 and 3) and vinyl acetate (Example 4).
However, the presence of such strong acid catalyst in the polyester product could lead to degredation of the product. Also, its presence may decrease the shelf life and pot life of coating systems produced from oligomers containing the polyester product and certain crosslinking agents. The use of a polyester product containing such strong residual acids may generate highly colored by-products that may be detrimental in some coating applications.
U.S. Pat. No. 4,188,472 describes reacting (a) a lactone with an ester-containing acrylyl or alpha-substituted acrylyl group and one or two hydroxyl groups and (b) reacting the product of (a) with an isocyanate. Specifically, in Examples I to III, hydroxyethyl acrylate is added to epsilon-caprolactone which was heated to 130.degree. C. (Example 1) or 120.degree. C. (Examples II and III). Large amounts of catalyst such as TPT titanate (greater than 2000 parts per million--Example I) or a mixture of stannous octoate and dibutyltin dilaurate (greater than 1500 parts per million--Examples II and III) were added to the reaction mixture. Additionally, the reaction carried out in these Examples utilizes large amounts of inhibitor, i.e., greater than 5000 parts per million. The reaction is carried out at temperatures of 130.degree. C. for 6 hours (Example I) and 120.degree. C. for 8 hours (Examples II and III). The product of the reaction in these Examples is described as having a hydroxyl value of 162 (Example I), 318 (Example II) and 122 (Example III). In Example II the reaction is stated to be complete. The epsilon caprolactone.hydroxyethyl acrylate product of Examples I, II and III was further reacted with a diisocyanate.
However, the use of the large amounts of catalyst and inhibitor in the polymerization described in U.S. Pat. No. 4,188,472 can have deleterious effects on the subsequent use of the lactone modified resin in polymerization or copolymerization reactions and/or crosslinking reactions.
Eureopean Patent Application No. 0044 393A2 titled "Process For Production of A (Meth) Acrylate Resin With Hydroxyl Groups and Modified by Epsilon-Caprolactone" describes the reaction of at least one monoester of acrylic or methacrylic acid with an alkane diol with 2-4 carbon atoms in the molar ratio of 1.5:1 to 1:3 with epsilon-caprolactone. The reaction is described as occurring at a temperature of 60.degree.-130.degree. C. in the presence of an organotin compound. Specifically, in Example I an adduct from 2-hydroxyethyl acrylate and dibutyltin oxide are heated to 120.degree. C. and epsilon-caprolactone is added over the course of two hours. This mixture is heated for two more hours at 120.degree. C. This Example was repeated and the reaction product was shown to contain greater than 25 weight percent of unreacted 2-hydroxyethyl acrylate. The epsilon caprolactone.hydroxyethyl acrylate product of Example 1 was further polymerized with methyl methacrylate, 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate.